Bone formation steadily declines with age resulting in significant loss of bone mass, and reactive oxygen species (ROS) are thought to be a major contributor to the aging process. H2O2 treatment significantly reduced bone nodule formation rate in pre-osteoblastic cell, MC3T3E1. In this study, to identify which genes have an altered transcription level associated with bone loss by ageing, MC3T3-E1 cells were treated with H2O2, and monitored gene expression change using the Affymetrix GeneChipTM system (Mouse; 34,000 genes). H2O2 altered many gene expressions including reduction of osteomodulin (OMD) mRNA level. The reduction of OMD gene expression by H2O2 was successfully confirmed by reversed transcription polymerase chain reaction (RT-PCR) and real-time PCR. Since OMD was found in bone tissues and play an important role in biomineralization, the reduction of OMD gene expression by H2O2 may be involved in the decline of bone formation in the ageing process.